a tiny sail boat ? lol, thats pretty fail
I would make an aircraft with/that floats so it can ditch in the sea if it conks out on a cloudy day, and just stay put in the water for however long it takes for a storm to pass (if it lands in one)
maybe plot a course so it lands on beaches or fields or whatever to recharge, since i thoroughly doubt a DIY'er can make a perpetual solar plane.